1. Field of the Invention
The present invention relates to a voltage regulator.
2. Description of the Related Art
First, a conventional voltage regulator is described. FIG. 4 is a circuit diagram illustrating the conventional voltage regulator.
The conventional voltage regulator includes an input terminal 71, a ground terminal 72, an output terminal 73, an output transistor 74, a voltage divider circuit 75, a reference voltage circuit 76, an amplifier 77, and a source follower circuit 78.
An operation of the conventional voltage regulator is described. When an output voltage Vout of the output terminal 73 increases, a divided voltage Vfb of the voltage divider circuit 75 increases. When the divided voltage Vfb becomes higher than a reference voltage Vref, a difference therebetween is amplified as an increased component, and hence an output voltage of the amplifier 77 increases. The output voltage of the amplifier 77 is input to a gate of the output transistor 74 through the source follower circuit 78. Then, the output transistor 74 is turned off to reduce the output voltage Vout. Therefore, the output voltage Vout is controlled to a desired constant voltage. Even when the output voltage Vout reduces, the output voltage Vout is controlled to the desired constant voltage in the same manner as described above (see, for example, JP 2001-195138 A).
The source follower circuit 78 operates to remove a ripple of an input voltage Vin.
However, according to the conventional voltage regulator, the source follower circuit drives the output transistor, and therefore an imbalance is created between a sink current and a source current with respect to the gate of the output transistor. Therefore, the conventional voltage regulator cannot achieve high-speed response.